Field of the Invention
The present invention relates to a drive transmission apparatus for a twin-screw extruder. In particular, it relates to an improvement that facilitates the adjustment of the gear power-transmission apparatus that transfers rotational power from a prime mover device to screws.
A twin-screw extruder is provided with two screws that are disposed parallel in close proximity. A drive transmission apparatus transfers a rotational driving force from a prime mover to the screws of the twin-screw extruder to cause the screws to rotate. The narrow spacing between the screws sets a limit on a diameter of a gear that is linked to the screws for transferring the rotation thereto. It is not possible to increase the diameter of the gear attached to at least one of the screws.
Since a drive transmission apparatus used in a twin-screw extruder transmits a high level of torque generated by a high-power input but a low rotational speed, the prior-art drive transmission apparatus makes use of gear trains such as those shown in FIGS. 6 to 10.
An example of such a prior-art drive transmission apparatus is shown in FIG. 6. A first screw 11 and a second screw 12 provided for the twin-screw extruder are disposed in parallel. A prime mover such as a motor 30 (which also includes reduction gears) is connected to an input shaft 31. A coupling portion 32 is provided on the end of this input shaft 31. A rear-end portion of a transmission shaft 33 is linked to a first linkage portion 32a of the coupling portion 32 so that the transmission shaft 33 is connected to the input shaft 31 via the coupling portion 32. A front-end portion of the transmission shaft 33 is connected to the first screw 11. A transmission shaft 41 is connected to the second screw 12. To sustain a thrust load from each of the first screw 11 and the second screw 12, thrust bearings 43 and 44 are provided on the ends of the transmission shafts 33 and 41, respectively.
A spur gear 34 is attached to the transmission shaft 33 on the side thereof opposite to the side that is linked to the first screw 11, with the configuration being such that the spur gear 34 is rotated in synchronization and together with the transmission shaft 33. An end portion of the spur gear 34 facing toward the motor 30 engages with a second linkage portion 32b formed in the coupling portion 32.
A side view of the drive transmission apparatus of FIG. 6 is shown in FIG. 7 and a section taken along the line VII--VII of FIG. 7 is shown in FIG. 8. As shown in FIG. 7, two idler spur gears 35 and 36 are provided at one end each of parallel idler shafts 37 and 38, respectively, in engagement with the spur gear 34. Two idler helical gears 39 and 40 are attached to the other ends of the idler shafts 37 and 38, respectively. Each of these idler helical gears 39 and 40 engage with a helical gear 42 that is attached to the transmission shaft 41 of the second screw 12. Therefore, the configuration is such that the rotation of the spur gear 34, which is connected to the input shaft 31 by the coupling portion 32, is transmitted to the transmission shaft 41 of the second screw 12 through the two parallel gear trains (in other words, the gear train consisting of the idler spur gear 35, the idler shaft 37, the idler helical gear 39, and the helical gear 42 and the gear train consisting of the idler spur gear 36, the idler shaft 38, the idler helical gear 40, and the helical gear 42), in such a manner that the second screw 12 rotates.
The teeth of the spur gear 34 and the idler spur gears 35 and 36 extend parallel to the transmission shaft 33 and the idler shafts 37 and 38. The helical gear 42 is configured in such a manner that it has teeth that are inclined in the same direction as those of the second screw 12. This is to ensure that part of the thrust loading that occurs when the second screw 12 is rotationally driven is borne by the idler helical gears 39 and 40 via the helical gear 42.
The first screw 11 and second screw 12 must be made to rotate in the same direction, at the same rotational speed. This is determined by factors such as the number of teeth of each of the gears that form the gear trains, the module of each gears, and intershaft distance.
It is necessary to adjust a phase of meshing of the gears and the tooth bearing thereof, to ensure that the two parallel gear trains (consisting of the idler spur gears 35 and 36, the idler helical gears 39 and 40, and the idler shafts 37 and 38) engage uniformly with the spur gear 34 and the helical gear 42, so that the rotational driving force is transferred uniformly to the first screw 11 and the second screw 12.
In this prior-art drive transmission apparatus, the four gears consisting of the idler spur gears 35 and 36 and the idler helical gears 39 and 40 engage together to form a gear transfer mechanism. Therefore, to adjust the meshing phase or tooth bearing of the gears, at least one of the four gears is adjusted as described below.
The configuration is such that one of the gears, such as the idler spur gear 35, can be released so that it no longer engages with the spur gear 34. The freeing of this idler spur gear 35 makes it possible to make the phase adjustment, etc. The idler spur gear 35 is constructed of two components, a ring-shaped gear portion 35a and a boss portion 57, as shown in FIG. 9. The ring-shaped gear portion 35a has a hole 50. A hub 51 of the boss portion 57 is designed to fit tightly into the hole 50. An annular oil groove 52 is provided in an inner peripheral surface of the ring-shaped gear portion 35a, extending in the circumferential direction thereof. This annular oil groove 52 is designed to form a sealed annular passageway together with the outer peripheral surface of the hub 51.
An oil passageway 53 that communicates with the annular oil groove 52 is formed in either the ring-shaped gear portion 35a or the boss portion 57. High-pressurized oil from a hydraulic power source (not shown in the figures) is supplied from this oil passageway 53 to enable the introduction of high-pressure oil into the annular oil groove 52. This high-pressure oil causes the inner circumference of the ring-shaped gear portion 35a to expand. As a result, a meshing phase adjustment becomes possible because the ring-shaped gear portion 35a can be made to rotate alone about the hub 51 of the boss portion 57. When the phase adjustment is completed, reamer bolts or knock pins 54 can be used to fix the ring-shaped gear portion 35a firmly with respect to the boss portion 57.
Another method that can be used for a meshing phase adjustment is shown in FIG. 10. A thin cylindrical portion 35c is formed integrally with the ring-shaped gear portion 35a in such a manner that it protrudes from the right-hand side thereof as seen in the figures. The boss portion 57 fits into a hole 35b of this thin cylindrical portion 35c in a manner as a clearance fit. An annular oil groove 52 is formed on an inner surface of the ring-shaped gear portion 35a, extending in the circumferential direction thereof. A gap is formed between the ring-shaped gear portion 35a and the boss portion 57 by forcing high-pressurized oil from an oil passageway 53 into the annular oil groove 52. Since this permits the ring-shaped gear portion 35a to rotate alone, it enables phase adjustment and the adjustment of tooth bearing. After the adjustment is completed, a tightening means, which consists of members such as two tightening rings 62 and 63 that fit over the thin cylindrical portion 35c with a tapered ring 60 therebetween, is tightened by using bolts 61. This tightening means ensures that the thin cylindrical portion 35c is firmly connected to the boss portion 57 by frictional force.
With the prior-art apparatus shown in FIG. 9, after the meshing phase and tooth bearing adjustment operation of the gears in the gear transfer mechanisms, in which the four linked gears (the idler spur gears 35 and 36 and the idler helical gears 39 and 40) are engaged, the aforementioned gears must be fixed in place using knock pins and bolts. This required work to fix the gears is an extremely complicated task. In other words, after the gears configuring the gear trains have been engaged and the drive transmission apparatus has been assembled for the first time, the idler gear 35, the boss 57 and reamer bolts or knock pin 54 must be removed from the gear trains to be made free. This freed gear is then disassembled and the phase, etc., thereof is adjusted. Subsequently, the idler gear 35 and the boss 57 must be fixed by using reamer bolts or knock pins. During this process, machining of the reamer bolts or knock pins is also necessary. The apparatus is then reassembled. In this manner, adjustment of the phase of meshing of the gears in the prior-art drive transmission apparatus not only necessitates time and labor, it also means that a large number of components are used in the configuration of the apparatus.
In addition, a twin-screw extruder for plastics is used at a torque that is close to the working limit of the transmission shaft. Since the connection between the gear portion 35a and the boss portion 57 in the prior-art apparatus of FIG. 10 is by friction, as described above, this means that reliability concerns make it difficult to use the apparatus over extended periods, unless there is considerable leeway in the torque.